A heat-conduction type batch microcalorimeter has been used for quantitative measurements of body fluid components. Measurements of chymotrypsin, pepsin, trypsin and lactate dehydrogenase were carried out using kinetic calorimetry. Measurement of total heat was used for quantitation of uric acid and total cholesterol. Differentiation of lactate dehydrogenase isoenzymes and free and esterfied cholesterol was accomplished. Studies are continuing on the calorimetric assays that employ antigen-antibody reactions.